1. Field of the Invention
The present invention relates to an image forming apparatus equipped with a removable cartridge.
2. Description of the Related Art
An image forming apparatus employing the electrophotographic technology prints an image in the following way. First, an image carrier (hereinafter, referred to as “photosensitive drum”) uniformly charged by a charging device is selectively exposed to light by an exposure device, and thereby a latent image is formed on the photosensitive drum. Then, the latent image is developed with a developer (toner) by a developing device, and the developed image is transferred onto a print medium. Thereafter, the transferred image on the print medium is fixed with pressure and heat by a fixing device, and thereby an image is printed on the print medium.
To allow an electrophotographic apparatus to form multicolor images, a configuration known as the “4-pass printing” configuration disclosed in U.S. Pat. No. 7,983,597 has been proposed and put into practical use. In the 4-pass printing configuration, plural fixed developing devices containing developers of different colors are provided around a single photosensitive drum, and form images of their respective colors on the photosensitive drum one after another. Then, the color images thus formed are overlaid one upon another on an intermediate transfer body. Thereafter, all the overlaid color images are together transferred onto a print medium to form a multicolor image on the print medium.
Such electrophotographic image forming apparatuses require maintenance work such as refilling of the toners and adjusting/replacing parts after a certain period of use. One of methods put into practical use to make the maintenance work easier is use of developer cartridges each formed as a unit including a toner and a developing device, and configured to be removably mountable in the image forming apparatus.
In addition, Japanese Patent Laid-Open No. 2010-078955 discloses another image forming apparatus configured to allow a larger-capacity image forming unit to be mounted in a space for mounting standard-capacity image forming units.